Why might that be? well to keep it simple, here are two possible reasons:

#1 When you run in traditional running shoes you land on your heel. When you run Barefoot or when you run wearing a Barefoot Running shoe (see my post – Are Barefoot Running Shoes an Oxymoron?) you land on your forefoot.

Some researchers say that landing on your heel is much harder on your body than landing on your forefoot.

#2 When you run the impact on your legs can be up to 12 times your body weight.

Some researchers say that when you run in traditional running shoes you put more force (shock – known as Impact Transient) on your feet and body than when you run barefoot.

Furthermore some suggest that the more cushion your running shoe has, the more force (shock) you inflict onto your feet and body.

From Born To Run page 173 – “at McGill University in Montreal Steven Robbins, MD and Edward Waked, Ph.D., performed a series of tests on gymnasts. They found that the thicker the landing pad the harder the gymnasts stuck their landings. Instinctively the gymnasts were searching for stability. When they sensed a soft surface underfoot, they slapped down hard to ensure balance. Runners do the same thing thing Robbins and Waked found…” (emphasis added).

First of all, barefoot running allows the foot to move, land, and absorb shock (referred to scientifically as the impact transient) naturally. Modern running shoes, while designed to prevent injury, actually increase the likelihood of injury largely by restricting the movement of the foot, and thereby allowing the foot musculature to atrophy. Squeezed and cushioned, the foot contributes little to running. Once barefoot, though, the foot can move naturally, and plays much more of an intricate role with every step.

All in all, the foot aids greatly in shock absorption that shod runners (who land on their heels 75% of the time) end up absorbing in their joints. Without the cushioning heel of a running shoe, the barefoot runner naturally strikes nearer the front of the foot, with either a “forefoot” or “mid-foot” landing. This means that the barefoot runner actually reduces the impact transient on the lower leg, which after thousands of heel strikes the cushioned-heel runner will undoubtedly feel. Next, the barefoot runner leans a little more forward than the shod runner, preserving momentum and getting more push off the foot itself. This makes for more efficient running, and less strain on the muscles of the upper leg.

Running shoes have also been shown to decrease actual running efficiency. Even lighter shoes add weight, which is in turn placed on the legs and joints, preventing a natural stride. The cushioning sole of a shoe also absorbs some of the spring of the foot, instead of transferring it directly to forward motion.”